Mercury (Hg) is a chemical element with atomic number 80. Its symbol Hg comes its Latin name hydrargyrum, which in turn comes from the Greek word hydrargyros meaning "water-silver". Mercury is sometimes also called quicksilver. It is a silver colored liquid metal and has the lowest melting point and boiling point of any stable metal.

Mercury has been known to Man for thousands of years and has been used for many things over the centuries. A tool still largely associated with mercury is thermometers, where liquid mercury within a glass tube expands when heated, thereby allowing us to read the temperature. However, since mercury is very toxic it is being phased out from most of its application, including thermometers.

There are several stable mercury isotopes, but ²⁰²Hg (80 protons and 122 neutrons) is the most abundant one.